The present invention relates to a method of drawing shapes and particularly to a method of drawing shapes, which is a method for aiding image drawing by computer graphics software for two-dimensional shapes and which is adapted to two-dimensional animation.
Cell-animation as a traditional technique was produced by the steps of: drawing immovable portions such as a background, etc. on paper; drawing movable portions such as a character, etc. on celluloid; and taking a photograph of a laminate of the paper and the celluloid by a camera. The step of drawing movable portions on celluloid was roughly classified into a process of keyframe drawing, a process of in-between drawing and a process of painting. In the process of keyframe drawing, frames serving as keys called keyframes were drawn on paper by rough line drawing. In the next process of in-between drawing, an in-between line drawing was made in between the keyframes on the paper by use of a careful line cleaned up. In the further process of painting, the animation image was transferred onto celluloid and painted at the back of the celluloid. On the other hand, a technique of digitized animation production advanced in recent years was a technique in which procedures on and after the process of painting were carried out by computer. That is, all animation images drawn on paper by manual work were fetched into a computer by a scanner, or the like, painted by painting software, or the like, and digitally synthesized with a background image.
That is, even in the digitized animation production, there was the existing condition that animation images were drawn on paper by manual work. The number of steps of the manual work was enormous. On the other hand, a technique of producing animation by fetching keyframes into a computer by a scanner, or the like, and by automatically in-betweening shapes between the keyframes by computer through generating graphics with reference to the keyframes was proposed as described in U.S. Application Ser. No. (not known), filed on Dec. 1, 1999 while claiming priority based on Japanese Patent Application No. 10-352258 filed on Dec. 11, 1998.
A technique using a Bxc3xa9zier curve is generally used for generating graphics. This technique is widely employed in drawing software. For example, this technique is described in Adobe Illustrator 8.0 Manual Japanese version, page 65. As shown in FIG. 9, a Bxc3xa9zier curve is generally generated by a method in which the cursor position at the push of a button of a pointing device such as a mouse, or the like, is regarded as the position of a vertex whereas the cursor position at the release of the button is regarded as one control point for the Bxc3xa9zier curve. On this occasion, the other control point is set in a position symmetrical with respect to the vertex. After the Bxc3xa9zier curve is generated, a desired shape is obtained by directly manipulating the vertex and the Bxc3xa9zier control points as occasion demands.
An auto-tracing function for automatically generating a Bxc3xa9zier curve on the basis of a fetched image is also known. This is a function for generating a Bxc3xa9zier curve on the basis of color gamut information of an image specified by clicking the pointing device at a point of the image. (for example, as described in pages 100 and 101 of a manual attached to the software title xe2x80x9cIllustrator 8.0 Edition Japanese versionxe2x80x9d sold by Adobe Systems Incorporated).
The Bxc3xa9zier control points needed to be directly manipulated for generating and reshaping the aforementioned general Bxc3xa9zier curve. There was a problem that much labor was required for directly manipulating the Bxc3xa9zier control points because there were two Bxc3xa9zier control points for one vertex.
On the other hand, the auto-tracing function had a problem that it was impossible to generate the Bxc3xa9zier curve exactly when there was a gap in the color gamut, that is, when the handwritten line drawing was broken discontinuously. The auto-tracing function had also a problem that it was difficult to obtain natural in-betweening results when automated in-betweening was performed by computer because the position of the vertex was generated automatically by computer.
An object of the present invention is to provide a method of drawing shapes, which is applied to software for fetching keyframes into a computer and drawing shapes while tracing the keyframes and in which control points for a Bxc3xa9zier curve need not be directly manipulated but the position of a vertex is designated by a user without problem even in the case where a line drawing of each of the keyframes is broken discontinuously.
According to an aspect of the present invention, a plurality of keyframes drawn on sheets of paper are first fetched into a computer. Then, a user traces the contour of the first keyframe by Bxc3xa9zier curves. On this occasion, the computer automatically generates Bxc3xa9zier curves successively on the basis of information of the positions of vertices of the Bxc3xa9zier curves and information of the keyframe fetched into the computer only by user""s designating points as the vertices successively. For automatic calculation, an optimum path for connecting the last designated vertex and the current cursor position to each other is obtained and approximated by a cubic equation, so that Bxc3xa9zier curves are generated on the basis of comparison of coefficients of terms in the equation with coefficients in the Bxc3xa9zier curves.
With respect to the second keyframe et seq., the vertices of the previously generated Bxc3xa9zier curves are moved so manually as to be placed on the contour of each keyframe. Further, when the neighborhood of the contour is dragged by a mouse, Bxc3xa9zier curves are calculated again so as to be fit for the dragged locus.